(1) Field of the Invention
The present invention relates to a liquid crystal display device using Light Emitting Diodes (LEDs) as backlights, and particularly to a thin and relatively-large liquid crystal display device in which uneven brightness is eliminated and which is used for a TV or the like.
(2) Description of the Related Art
Liquid crystal display devices are being used in various fields because they can be made thinner and lighter. Liquid crystal itself does not emit light, and thus backlights are arranged on the back face of a liquid crystal display panel. Fluorescent lamps had been used as backlights for liquid crystal display devices with relatively-large screens such as TVs. However, LEDs are beginning to be used due to demands of thinner liquid crystal display devices and wider color display areas.
Light sources of backlights are arranged in a direct type method in which the light sources are arranged immediately below a liquid crystal display panel, and in a side-light type method in which the light sources are arranged on the side of a light guiding plate. The direct-type light sources have been used in many cases in a liquid crystal display device with a relatively-large screen in order to improve brightness of the screen. However, it is difficult to reduce the thicknesses of the backlights in the direct type. On the other hand, if the screen becomes large in size, the brightness cannot be sufficiently improved, or the backlights cannot be made thinner because the light guiding plate itself becomes thicker in the conventional side-light type method.
Accordingly, there has been developed a configuration in which a light guiding plate of a backlight device is divided into a plurality of blocks, and LEDs are arranged in each block. Japanese Patent Application Laid-Open No. Hei 11-288611 describes a configuration in which light guiding plate blocks divided as planar light source devices each having a large light-emitting area are tandemly arranged. Japanese Patent Application Laid-Open No. Hei 11-288611 describes that in consideration of a difference between both ends and a middle portion of each fluorescent lamp as a primary light source arranged in each light guiding plate block, a tongue-surface superposition portion having notches is formed at a superposition portion between the light guiding plates which are adjacent to each other in order to prevent generation of insufficient brightness of electrode portions on the both ends of the primary light source.
Further, Japanese Patent Application Laid-Open No. 2004-265635 describes a configuration in which an acrylic plate is arranged between a light guiding plate and a diffusion plate in order to prevent generation of uneven brightness at connecting portions between light guiding plate blocks which are tandemly arranged. Further, Japanese Patent Application Laid-Open No. 2004-265635 describes a configuration in which a predetermined distance is set between the light guiding plate and the diffusion plate if the acrylic plate is not used.
On the other hand, it is necessary to arrange LEDs in each block of the divided light guiding plate. LEDs are classified into a general top-view type LED which emits light from the upper side of a package and a side-view type LED which emits light from the side of a package. The side-view type LED is beginning to be used for a liquid crystal display device.
Japanese Patent Application Laid-Open No. 2005-317820 describes a configuration in which LED chips in a package are coupled to each other not through wire bonding but through a conductive adhesive in the side-view type LED, so that the size of the LED package is reduced. Japanese Patent Application Laid-Open No. 2008-198807 describes a configuration in which a lead frame is used for coupling an LED package to a wiring substrate in the side-view type LED, and the area of the lead frame is increased by branching the lead frame to improve heat radiation efficiency from an LED.
Japanese Patent Application Laid-Open No. 2003-234507 describes a configuration in which when the side-view type LED is mounted using solder, a plurality of portions are coupled by soldering in order to prevent displacement and inclination due to contraction of solder.